: With report of a susceptibility gene (ApoE) linked to late-onset Alzheimer's disease (AD), intense controversy has surrounded the issue of presymptomatic testing for this disorder. Although the scientific community has not endorsed ApoE testing for prediction of risk in asymptomatic individuals, a test is already being commercially marketed. This situation is likely to broaden as the Human Genome Project progresses. The investigators plan to develop an information base on how the public, particularly those at increased risk, comprehend the current information regarding inheritance of AD risk, understand the role of competing risk factors, and view such testing. In addition physician understanding and interest in genetic testing for AD will be studied. Specific aims also include comparison of respondent and physician expectations of the testing process. The investigators rely on survey methodology using previously tested lines of questioning. Participants will include adult offspring (n=700) of previously studied AD patients and physicians (N=335) who treat these patients. The proposed study focusses on knowledge of AD genetic risk and attitudes toward presymptomatic genetic testing where false negatives and false positives are a prominent feature. The investigators are concerned with personal characteristics associated with interest in testing, with emphasis placed on tolerance for test uncertainty (TTU) as a strong predictor of test acceptance. Focus groups of high risk offspring and physicians will be conducted to explore the educational needs of these populations. The results of this study provide basic knowledge applicable to genetic testing for complex diseases in which inherent genetic heterogeneity and incomplete penetrance affect the sensitivity and positive predictive value of genetic tests, yet because of commercial pressure and high public demand such testing becomes widely utilized.